The effective skid resistance of roadway pavements and surfaces is obviously a very important characteristic of the roadway surface, especially in terms of safety. Thus, there has been and continues to be a need for testing devices to test the effective skid resistance of a roadway pavement or surface or to test pavement specimens being developed.
At North Carolina State University in Raleigh, N.C., a pavement testing device has been developed and this is referred to as a variable speed friction skid tester, and is of the pendulum type. Basically the variable speed friction tester includes a pendulum with a rubber tire secured to a remote lower end thereof. In use, the pendulum is lifted to one side of its pivot point and allowed to swing past a pavement surface disposed in the pendulum's swing path such that the rubber tire passes generally tangential thereover. Because the wheel is locked in at least one direction, it contacts the pavement surface and skids thereover. By measuring the magnitude of the pendulum's movement past the pavement surface, one can determine the energy lost in friction due to the skidding and sliding movement of the rubber tire over the pavement, and this can be converted to a measurement that represents the effective skid resistance of the pavement being tested. Such a tester is suitable for laboratory test on pavement samples as well as actual field tests on highway surfaces.
The variable speed friction tester being referred to above enables one to predict the effect of the vehicle's speed on the skid resistance of wet pavements and to determine the effective skid resistance of actual pavement surfaces.
But with the variable speed friction tester and other conventional skid testers such as the conventional skid trailer and the British portable tester, individuals utilizing the testing devices have found it difficult to calibrate the various test machines and consequently the results of such tests sometimes lack total meaning and consequently cannot be totally understood, appreciated and used in determining the real effective skid resistance of a pavement surface. Thus, there exists a real need for a standard surface for calibrating skid testing devices.